1. Field of the Invention
An aspect of the present invention relates one of an electromechanical conversion element, a liquid drop ejection head, a liquid drop ejection device, and an image forming apparatus.
2. Description of the Related Art
Conventionally, such a liquid drop ejection head is known which includes a nozzle for ejecting a liquid drop, a pressurization chamber communicating with such a nozzle and containing an ink, etc., (an “ink” below) to provide a liquid drop, and an electromechanical conversion element such as a piezoelectric element or an electrothermal conversion element such as a heater, as a driving source for pressurizing an ink in such a pressurization chamber, or an energy generation part composed of a vibration plate for forming an ink flow channel and electrodes opposing it, wherein an ink in the pressurization chamber is pressurized by energy generated in the driving source or energy generation part to eject an ink drop from the nozzle. Additionally, such a pressurization chamber may also be referred to as an ink flow channel, a pressurization liquid chamber, a pressure chamber, an ejection chamber, or a liquid chamber, etc.
For an actuator which is used or may be used as such a driving source, a film structure such as a semiconductor device or an electronic device is known (see, for example, Japanese Patent Application Publication No. 2004-186646, Japanese Patent Application Publication No. 2004-262253, Japanese Patent Application Publication No. 2003-218325, Japanese Patent No. 3249496, Japanese Patent No. 3472087, Japanese Patent Application Publication No. 11-195768, Japanese Patent No. 4099818, Japanese Patent No. 3806127, Japanese Patent Application Publication No. 2003-282987, Japanese Patent Application Publication No. 2009-224368, Japanese Patent No. 4220459, Japanese Patent No. 3782401, Japanese Patent No. 4011334, and Japanese Patent Application Publication No. 2002-94018). For such an actuator, for example, two kinds thereof, that is, a piezoelectric actuator being used in a longitudinal oscillation mode in which a piezoelectric element expands or contracts in an axial direction thereof and a piezoelectric actuator being used in a flexural oscillation mode, have been in practical use.
For a piezoelectric actuator being used in a flexural oscillation mode, for example, a piezoelectric element is known which is formed by forming a uniform piezoelectric material layer over an entire surface of a vibration plate by a film formation technique and cutting such a piezoelectric material layer into a shape corresponding to a pressure generation chamber by a lithography method so as to provide each independent pressure generation chamber.
When a vector component of a spontaneous polarization axis of a piezoelectric film is coincident with a direction of an applied electric field in such a piezoelectric actuator, stretching caused by an increase or decrease in an intensity of an applied electric field may occur effectively to obtain a large piezoelectric constant, and hence, it may be most preferable to coincident a spontaneous polarization axis of a piezoelectric film with a direction of an applied electric field completely. Furthermore, it may be preferable to provide a small dispersion of an in-plane piezoelectric performance of a piezoelectric film in order to suppress a dispersion of an amount of an ejected ink, etc. When such a matter is taken into consideration, a piezoelectric film with an excellent crystal orientation may be preferable.
For a technique with respect to a crystal orientation, for example, a technique for film-forming a piezoelectric film on a Ti-containing noble metal electrode with an island-like Ti deposited on a surface thereof, thereby film-forming a piezoelectric film with an excellent crystal orientation (see, for example, Japanese Patent Application Publication No. 2004-186646), a technique for using a MgO substrate as a substrate thereby film-forming a piezoelectric film with an excellent crystal orientation (see, for example, Japanese Patent Application Publication No. 2004-262253), and a technique relating to a method for manufacturing a ferroelectric film wherein an amorphous ferroelectric film is film-formed and subsequently the film is crystallized by a rapid heating method (see, for example, Japanese Patent Application Publication No. 2003-218325) are known.
In many of such techniques, a PZT is fabricated on Pt, but, in such a case, it may be possible for an electrical characteristic such as a piezoelectric characteristic to be degraded, and hence, an electrode material of electrically conductive oxide such as RuOx or IrO2 has been studied in a field of a ferroelectric memory, etc.
Among them, a strontium ruthenium oxide (SRO) has the same perovskite-type crystal structure as a PZT, and hence, may be excellent in a bonding property at an interface, be easy to realize epitaxial growth of a PZT, and also be excellent in a characteristic of a Pb diffusion barrier layer.
However, excess Pb contained in a PZT may react with Sr or Ru contained in a strontium ruthenium oxide to form a compound having an electrical conductivity. Accordingly, a withstand voltage of a PZT may be very bad to facilitate leaking thereof, and hence, an electrical characteristic such as a piezoelectric characteristic may be degraded. For a matter relevant to such a thing, for example, it is reported in detail that an influence with an amount of excess Pb in a PZT may also be provided wherein it may be possible to suppress Sr diffusion after post-annealing in a case of a less amount of excess Pb (see, for example, Jpn. J. Appl. Phys. Vol. 40 (2001) pp. L346-348). Furthermore, when a PZT is fabricated by a solution method such as a spin-coat method, a thermal process at a crystallization temperature of 550° C. or higher may be involved and it may also be possible to suppress Sr diffusion depending on a baking temperature or a baking time at such a case. However, when an amount of excess Pb is in the range as described in the above-mentioned report, a sufficient initial deformation may not be obtained in a case where use is made as a piezoelectric actuator and a deficiency of degraded deformation may occur in a case where a continuous operation is further conducted.
For a technique using strontium ruthenium oxide having a perovskite structure, there are provided, for example, a technique relating to a semiconductor device having at least one of upper and lower electrodes including a SRO and a capacitor configured to interpose a dielectric film (technique A: see, for example, Japanese Patent No. 3219496), a technique relating to a structure for which an epitaxial film (100) based on a SRO is fabricated on a Si (100) substrate so that its surface roughness (average roughness) is 10 nm or less (technique B: see, for example, Japanese Patent No. 3472087), and a technique relating to a structure including a perovskite-type oxide film for which a SRO is sputtered for film formation to fabricate amorphous films as lower and upper electrodes without actively heating a substrate and subsequently is annealed at a crystallization temperature (technique C: see, for example, Japanese Patent Application Publication No. 11-195768).
However, although an RTA treatment for formation of a SRO film is conducted after film formation at a room temperature in technique A, it could be found that it may be difficult to obtain (111) orientation when a PZT is fabricated on a SRO. Furthermore, it has been found that when a thickness of a SRO film is 10-20 nm, it may not possible to obtain a sufficient initial deformation in case where use is made as a piezoelectric actuator and a deficiency may occur in a case of a further continuous operation.
Furthermore, although a SRO is used for a lower electrode in technique B, there is no description of a SRO being used for an upper electrode. From the viewpoint of the above-mentioned characteristic of a SRO as a Pb diffusion barrier layer, it may be preferable to use a SRO also for an upper electrode. Furthermore, although a ferroelectric film fabricated on an epitaxial film (100) has (100) orientation, it could be found that (111) orientation of a piezoelectric film may be preferable in order to suppress degradation of a deformation characteristic in a case where a continuous operation is conducted as a piezoelectric actuator while it may not be possible for (100) orientation to suppress such a degradation sufficiently.
Furthermore, in technique C, it could be found that it may be difficult to obtain (111) orientation in a case where a PZT is fabricated on a SRO and degradation more than an initial deformation may be caused in a continuous operation in a case where use is made as a piezoelectric actuator, so that a deficiency may be caused.